Gandalf
To come back from the dead in a spectacular fashion, normally just in time to save someone's ass from getting kicked. Just like Gandalf in LOTR.
Example:
I was sure he was dead after the nuke went off, but he did a Gandalf and saved Bauer's ass.
I was sure he was dead after the nuke went off, but he did a Gandalf and saved Bauer's ass.